1. Field of the Invention (Technical Field)
The present invention relates to methods and apparatuses for determining the velocity, temperature and pressure of gases in supersonic inlets of scramjet engines, and any other gas flows requiring the knowledge of pressure, velocity and temperature.
2. Description of Related Art
Note that the following discussion refers to a number of publications by author(s) and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-a-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
Turbine-based combine cycle (TBCC) and rocket-based combined cycle (RBCC) are airbreathing propulsion technologies for two-stage-to-orbit vehicles that operate at costs lower than conventional methods based solely on rockets and scramjets. TBCC is applicable in the flow regime from subsonic to supersonic and not suitable for orbital insertion, but is the choice for a high speed passenger transport (Sippel, M. and Okai, K., “Preliminary Definition of a TBCC Propulsion System for a Mach 4.5 Supersonic Cruise Airliner,” ISABE 2007-1204, International Society for Air Breathing Engines). RBCC is suitable for hypersonic to rarefied flow regimes. RBCC based vehicles are capable of reaching high altitudes and space with pure rocket operation (Kloesel, K. J., Ratnayake, N. A., and Clark, C. M., “A Technology Pathway for Airbreathing, Combined-Cycle, Horizontal Space Launch Through SR-71 Based Trajectory Modeling,” AIAA 2011-2229, 17th AIAA International Space Planes and Hypersonic Systems and Technologies Conference, San Francisco, Calif.). The need for the non-intrusive measurement of velocity, pressure and temperature profiles at the inlet and exhaust flows is obvious when supersonic flow speeds are present. Traditional probes used for temperature, pressure and velocity disturb the flow sufficiently that corrections, based on a priori measurements and models, are needed to ascertain the local flow properties. Moreover, wall-based measurements of pressure do not provide information on local nonuniformities. Even in uniform flows, pressure in the core flow is determined via corrections using models with the knowledge of the adjacent wall pressure. Temperature and velocity measurements based on optical methods such as particle imaging velocimetry (PIV) and planar laser-induced fluorescence (PLIF) are excellent for a small region of interest but not easily amenable to a full profile of the inlet and exhaust flows. Accurate information of inlet flow properties is important for gauging the mass capture and properly tuning the fuel flow for efficient combustion. Flow properties of exhaust flows are important for assessing the thrust generated by the combustion system (Drummond, J. P., Cockrell, C. E., Jr., Pellett, G. L., et al., “Hypersonic Airbreathing Propulsion—An Aerodynamics, Aerothermodynamics, and Acoustics Competency White Paper,” NASA/TM-2002-211951).
Velocity and temperature measurements via tunable diode laser absorption spectroscopy (TDLAS) are well established for measuring gas temperatures and velocities in combustor flows. Both direct absorption and wavelength modulation spectroscopy (WMS) methods exist to make these measurements (Hanson, R. K., “Applications of quantitative laser sensors to kinetics, propulsion and practical energy systems,” Proc. Combust. Inst. 33, 1-40 (2011); Li, F., et al., “Uncertainty in velocity measurement based on diode-laser absorption in nonuniform flows,” Appl. Opt. 51, 4788-4797 (2012); Barhorst, T., Williams, S., Chen, S.-J., Paige, M. E., and Silver, J. A., “Development of an In Flight Non-Intrusive Mass Capture System,” AIAA Paper No. 2009-5067, 45th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit (2009); Silver, J. A., “Frequency Modulation Spectroscopy for Trace Species Detection Theory and Comparison Among Experimental Methods,” Appl. Opt. 31, 707-717 (1992); Bomse, D. S., Stanton, A. C., and Silver, J. A., “Frequency Modulation and Wavelength Modulation Spectroscopies: Comparison of Experimental Methods Using a Lead-Salt Diode Laser,” Appl. Opt. 31, 718 (1992)). These studies always require the recording of the full absorption spectrum, and for temperature measurements often require two lasers. For high speed (>1 kHz) transient measurements, the electronic requirements for high precision and sensitivity become cumbersome at best, where data acquisition rates and demodulation electronics push beyond MHz frequencies. The analyses of these measurements can be quite complex, requiring measurement of a host of spectroscopic parameters and their dependence on temperature and pressure in order to retrieve the local gas temperature. This makes the sensor systems inflexible and suitable for only one gas, whereas multiple gases may be of interest. All of the aforementioned measurements apply to velocity or temperature. There have been no reported methods to optically measure local pressure.
Hanson (U.S. Pat. No. 5,178,002) discussed a system and method for determining the value of thrust non-intrusively from products of combustion of a jet engine. Both line-of-sight absorption spectroscopy and laser-induced fluorescence methods are discussed for measuring pressure, velocity, and temperature of a gas. Full absorption spectra are used in the measurements.
Williams, S., et al., “Diode Laser Diagnostics of High Speed Flows,” AFRL-PR-WP-TP-2007-204, Air Force Research Laboratory, Propulsion Directorate, October 2006, discussed the use of direct absorption spectroscopy with full line shapes and multiplexing of multiple lasers for the measurement of mass capture in hypersonic inlets and isolators.
Lindstrom, C., et al., “Diode Laser Absorption Tomography of 2D Supersonic, Flow,” 43rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 8-11 Jul. 2007, Cincinnati, Ohio, examined the combined use of tomography reconstruction techniques and direct absorption spectroscopy with full line shape to probe supersonic flows for determining flow properties and species concentrations.
Chen, S.-J., et al., “Laser-Based Mass Flow Rate Sensor Onboard HIFiRE Flight 1,” 45th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 2-5 Aug. 2009, Denver, Colo., used wavelength modulation spectroscopy with second harmonic detection and full line shape to measure gas velocity in high speed flows. The measurements were carried onboard a sounding rocket reaching a speed of Mach 8.
Wheatley, B., “Tunable Diode Laser Absorption Spectroscopy of Hypersonic Flows,” 28th International Congress of the Aeronautical Sciences,” ICAS, 2012, reviewed the method of tunable diode laser absorption spectroscopy for the measurement of flow properties and species concentrations in hypersonic and scramjet flows. Direct absorption spectroscopy and wavelength modulation spectroscopy using first and second harmonic detection, using full line shape, were compared.
Girouard, R., et al. (U.S. Pat. No. 8,265,851) disclosed a method for controlling the performance of engines via the measurement of a wavelength-dependent parameter. Based on the measured parameter, a needed adjustment to the combustion event is determined and physically applied to the engine to enhance engine performance. Direct absorption spectroscopy and wavelength modulation spectroscopy were identified as some of the measurement methods to obtain velocity, temperature, and species concentrations, all using full line shapes.
The present invention improves on the art by, e.g., using an optical velocity measuring system that comprises a light source from a diode laser and two detectors to monitor two crossed-beams paths. Alternatively, pressure can be measured using a single path across the flow. The present invention provides the following advantages over the state-of-the-art sensors: (1) not requiring the need to scan the full absorption line shape; (2) no need to fit the data to obtain peak positions of measured absorption line; (3) no modeling of line shapes to account for residual amplitude modulation; (4) capable of achieving high-bandwidth measurements of 10 kHz or higher; (5) measuring only two point values per probed path; (6) inherently self-calibrating; (7) no contributions from interference fringes (etalons) which show up only as dc offset; and (8) high-sensitivity using wavelength modulation spectroscopy with 1f detection.